An animal model tumor system will be used to develop a series of assay methods designed to dissect and evaluate various parameters involving the interaction between a host's immune system and a growing neoplasm. Adsorption of a population of lymphocytes to an appropriate control or target cell monolayer, or to such a monolayer coated with specific antibody or antibody and certain complement components will allow a direct enumeration of the proportion of lymphocytes capable of recognizing either antigen, antibody-coated or antibody-complement coated cells. The feasibility of using a fluorescein transfer assay to quantitate cytotoxicity will be determined. A correlation between cytoplasmic bridge formation and cytotoxicity will make it possible to directly quantitate the number of lymphocytes adhering to an appropriate monolayer which are also capable of participating in a cytotoxic reaction, as well as providing further insight into the cytotoxic reaction. In the absence of such a correlation, cytotoxicity will be determined by Cr51 or I125-iododeoxyuridine release. Elution of adsorbed lymphocytes will provide a highly enriched population of the appropriate "sensitive" lymphocytes, permitting the determination of the effects of antigen, antibody or antigen-antibody complexes on both the recognition and cytotoxic reactions of the various populations of lymphocytes. The possible cytotoxic effects of humoral antibodies will be determined by means of a microcytotoxicity test. Following the development of the necessary technology, an attempt will be made to apply our assay system to human breast cancer to explore the following: (a) the possibility of developing a method of cancer detection or evaluation, and (b) the utilization of our assays in developing an understanding of the precise relationship between host and tumor in tumor-bearing individuals. A further attempt will be made in the animal model system to acquire specifically labeled anti-tumor antibody and labeled tumor specific antigen. With these reagents a study will be undertaken of the mechanism of enchancement with respect to each sensitized lymphocyte population at the cellular and molecular levels.